The invention pertains to the reinforcement of concrete beams or panels and, in particular to a dowel strip acting as a bent-up bar in reinforced concrete beams or panels, the dowel strip 4A (see FIG. 4) consisting of a bottom strip and a plurality of dowels 6A perpendicularly welded to the strip at one of their ends 5A, each dowel having a dowel shank 7A and, on their upper ends, a dowel head 8A that is wider than the dowel shank, whereby the dowel shank has ribs on at least part of its surface.
Known dowel strips of this kind (DE-PS 27 27 159.6) serve as bent-up bars in reinforced concrete beams and panels at points of support, particularly in the vicinity of column connections of the beam 1 with vertical columns 2, i.e. connections to absorb the lateral forces occurring in these areas due to stress created by the vertical columns.
In a reinforced concrete beam or concrete panel reinforced in this fashion, an internal compression force grid is formed in the column area, the pattern of which resembles a truss, the truss components of which are referred to with the terms customarily used for trusses.
Longitudinal reinforcement bars 3 provided near the topside of the beam or panel each act as form a tension chord component of the force truss in the area of the columns. The dowels 6A of the dowel strip located perpendicular to these tension chord components represent the vertical tension components of the force truss. The concrete that is in compression on the underside of the beam or the panel in the vicinity of the columns, assumes the function of the compression chord component 11 of the force truss, but this function may also be assumed by the dowel strips if the strips extend in the longitudinal direction of the beams. Between (i) the dowel heads on top and the points of support of the column or the dowel strips of adjacent additional dowels, sloped strut component 10 of the force truss are formed in the concrete.
The formation of a joint of the force truss at the dowel head or strip, respectively, requires that the vertical tension component 6A be transferred all the way to the dowel head or strip, respectively, so that the differential forces can be transferred to the tension chord component 3 or the compression chord component 11, respectively through a positive enclosure by the concrete.
In the known dowel strips, the dowel shank 7A is designed smooth and cylindrical as shown in FIG. 4; the resulting relatively minor adhesion between the dowel shank and the concrete results in the force of the vertical tension component 6A being transferred until it reaches the dowel head or dowel strip, respectively.
The sloped main tensile stress 10 forming in the concrete leads to the formation of shearing cracks 12 in the concrete extending approximately along the sloped strut components 10, whereby the width of the cracks restricts the load carrying capacity of the beam or panel.
According to a known reinforcement technique, the width of unavoidable shearing cracks in the concrete is limited and the carrying capacity of the structural beam increased by inserting additional bent-up bars essentially extending perpendicular to the expected direction of the cracks.
In a beam or panel equipped with dowel strips serving as bent-up bars, according to this prior art theory, either the bent-up bars consisting of dowel strips would be reinforced by using more or larger diameter dowels, or a separate, additional bent-up bar would be inserted to limit the width of the cracks. Both measures, however, involve additional material and labor costs.
In a known dowel strip of the above kind (EP-A-495 334), the dowels are made from ribbed reinforcement bar; the dowel shank has ribs on its surface. The vertical tension member force acting inside the dowel shank is thus not at all or only to an insignificant extent transmitted to the end of the dowel, with the result that the desired formation of a truss framework joint at the dowel ends is impaired.
The aim of the invention is therefore to design a dowel strip configuration to effectively limit the width of the cracks in the concrete without additional material or labor expenditures while maintaining the effective formation of truss framework joints at the dowel heads.